The present invention relates to an electric motor controller in an electric compressor. Specifically, the present invention relates to an electric motor controller installed in an electric compressor that compresses and discharges refrigerant in a compression chamber by compressing action of a compression member based on rotation of a rotary shaft rotated by the electric motor, and cools coils of the electric motor with the refrigerant.
To protect coils of the electric motor in an electric compressor from electrical breakdown due to overheating, a measure has been proposed in which the electric compressor is stopped before the coils are overheated. Japanese Laid-Open Patent Publication No. 2001-280259 discloses a compressor that includes a first temperature detection section for detecting the temperature of the coils of an electric motor and a second temperature detection section for detecting a temperature lower than the detection temperature of the first temperature detection section. When the temperature of the coils reaches the detection temperature of the second temperature detection section, the compressor is operated to increase its displacement. When the temperature of the coils surpasses the detection temperature of the first temperature detection section, the compressor is stopped.
However, if the electric compressor is stopped, the flow of refrigerant is stopped. This reduces the rate of decrease in the temperature of the coils, and thus extends the stopping period of the electric compressor. Therefore, the control, which stops the electric compressor, is not preferable.
When an electric compressor is activated, a control for maximizing the displacement (maximum load operation) is normally performed. For a certain time after the activation, the amount of refrigerant circulation for cooling the coils is not sufficient. Therefore, if the ambient temperature is high when the electric compressor is activated, since the maximum load operation supplies a current of a maximum current value to the coils, the temperature of the coils are raised before coolant lowers the coil temperature. As a result, the coil temperature reaches a stop Temperature set for preventing overheating after a short period from the activation. This stops the electric compressor.